Model A1418 / Late 2012 / 2.7 & 2.9 GHz Core i5 or 3.1 GHz Core i7 Processor

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Black screen after hard drive replacement

I followed the guide on this iFixit for replacing the hard drive on my iMac model but when I reconnected everything and turned on the Mac, you could hear the classic dong boot but the screen remained black. I tried to connect with the adapter to an external monitor, but it is always black. If earlier worked perfectly without any problem, what could have happened? I tried all combinations of keys at startup, but nothing has changed .... helppppp !!!

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Did an external monitor work before? You are not getting a signal out of the GPU if it did.

Remove the frame and observe and report the finding on the diagnostic LEDs to the right of the RAM slots.

UPDATE 3/10/16

LED 1 - Indicates that the trickle voltage from the power supply is detected by the main logic board. This LED will remain ON while the iMac is connected to the AC power. The LED will remain on even when the computer has been shut down or put to sleep. The LED will turn off only if the AC power is disconnected or the power supply is faulty.

LED 2 - Indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 - Indicates that the computer and the video card are communicating. This LED will be ON when the computer is communicating properly with the video card. If LEDs 1 and 2 are ON and you heard the startup sound, but LED 3 is OFF, then the video card might be installed incorrectly or need replacement.

LED 4 - Indicates that the computer and the LCD display panel are communicating. This LED will be ON when the computer is turned on and video signal is being generated. If the LED is ON and there is no image on the LCD display panel, the LCD display panel or inverter might be installed incorrectly or need replacement.

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Thank you for your answer Mayer,

i tried to connect an external monitor but not me 'no video signal. The classic "dong" boot feels. I opened the front panel and the LED on the motherboard lights up, there is always room for another ram? If you where?

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Comments:

There are four LEDs. Di just the first one light?

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Just opened on the panel board see only one LED on!

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Your power supply has failed or is not connected.

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But the startup "Dong" you hear when you start!

Where I find the power connector?

Thank!

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Display translations for but the "bong boot" is heard!

Translate instead but the boot "dong" is heard!

Nam hoc cogitem et ponam in te

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